Method for applying powder coatings to articles



c- 30, 1969 N. R. WALLIS 3,486,921

METHOD FOR APPLYING POWDER COATINGS TO ARTICLES Filed Oct. 31, 1966 5 Sheets-Sheet 1 INVENTOL NEIL. RuDOLPH M61413 3 Mdhmu lav-ramble s Dec. 30, 1969 N. R. WALLIS METHOD FOR APPLYING POWDER COATINGS T0 ARTICLES Filed Oct. 51, 1966 5 Sheets-Sheet 2 N. R. WALLIS Dec. 30, 1969 METHOD FOR APPLYING POWDER COATINGS TO ARTICLES Filed Oct. 31, 1966 5 Sheets-Sheet 5 INVENTaL N514. K M$O f LJHLL! s i M! Mm Dec. 30, 1969 N. R. WALLIS 3,486,921

METHOD FOR APPLYING POWDER COATINGS TO ARTICLES Filed Oct. 31, 1966 5 Sheets-Sheet 4 new INve/vr L MJMW 4mm s.

Dec. 30, 1969 N. R WALUS 3,486,921

METHOD FOR APPLYING POWDER COATINGS TO ARTICLES Filed Oct. 31, 1966 5 Sheets-Sheet 5 I l I l 1 1 I I l l l l n I I J IN V N IL NEIL.- PuDoLfH LJBLLIS f97'ranu27 United States Patent 3,486,921 METHOD FOR APPLYING POWDER COATINGS TO ARTICLES Neil R. Wallis, Cariad, Goring-on-Thames, England Filed Oct. 31, 1966, Ser. No. 590,851 Claims priority, application Great Britain, Nov. 12, 1965, 48,020/ 65 Int. Cl. B44c 1/06; Bc 5/00 US. Cl. 117-24 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to methods and apparatus for applying powder coatings to articles. It is more particularly concerned with processes in which finely divided coating materials are deposited on surfaces of the article to be coated under the influence of an electrostatic field.

It is an object of the invention to provide a method and corresponding apparatus suitable for the continuous coating of large numbers of similar articles.

One of the major problems associated with the use of coating materials in the form of solid particles is the prevention of the escape of powder into the air surrounding the apparatus used for the coating process and its deposition on the skin and clothing of operating personnel, also on the surfaces of nearby structures.

The invention aims to deal with this problem by carrying out the coating of the articles within an enclosure provided with entry and exit openings for the articles, and by restricting the egress of powder through these openings.

According to the invention there is provided a method for applying powder coatings to articles, wherein the articles are conveyed through the enclosure provided with entry and exit openings, wherein the articles are so conveyed through a plurality of streams of coating powder sprayed into the enclosure in the direction of the articles and forming with the air in the enclosure a fine cloud of the powder particles suspended in the air, wherein said cloud is maintained in continual rotational movement in the enclosure, and wherein the escape of powder not adhering to the articles is restrained by an inward flow of a gaseous medium through each of said openings, said inward flow being so directed as to promote said rotational movement.

The gaseous medium is conveniently air drawn from the external atmosphere.

The inward flow referred to may be produced by keeping the pressure in the enclosure below atmospheric pressure by withdrawing air from the enclosure.

The method may then take a form wherein the air is withdrawn from the enclosure at a rate in excess. of that necessary to maintain the required degree of subatmospheric pressure in the enclosure, wherein the air is so withdrawn in one or more streams which or each of which is subsequently divided into two sub-streams of which one contains substantially all of the non-adhered coating powder which has been withdrawn from the enclosure in suspension in the stream of withdrawn air and Patented Dec. 30, 1969 ICC the other contains the balance, if any exists, of said powder, and wherein the first sub-stream is recycled to the enclosure while the second is discharged to the external atmosphere by way of filter means which denude it as far as possible of any residual powder contained in it.

The method preferably takes a form in which the first sub-stream reenters the enclosure in the form of jets which are so directed as to promote said rotational movement of the cloud.

In this event the form of the method may further be one wherein some of the jets are directed from locations within the enclosure close to one side edge of the relative opening, the paths of the jets being transverse to the path of travel of the articles through the enclosure and the jets being directed towards said path obliquely to the general plane of the relative opening, and also wherein others of the jets are directed from locations within the enclosure close to the other side edge of the relative opening, the paths of said other jets being transverse to the path of travel of the articles through the enclosure and said other jets being directed away from said path oblique- 1y to the portion of the wall of the enclosure adjacent to the relative opening.

The jets aforesaid may co-operate in promoting the rotational movement of the cloud with balfie means located at selected positions around the enclosure interior.

The invention includes apparatus for applying powder coatings to articles, including an enclosure provided with entry and exit openings for the article, means for conveying the articles along a predetermined path through the enclosure, means within the enclosure for directing a plurality of streams of coating powder towards said path, the powder of said streams forming with the air in the enclosure a cloud composed of said powder in suspension in said air, means for maintaining said cloud in continual rotational movement in the enclosure, filter means and means for withdrawing air from the enclosure and discharging the same via said filter means to the eternal atmosphere at a rate sufiicient to maintain the pressure within the enclosure below that of the atmosphere outside, the reduced pressure thus maintained within the enclosure being such as to result in an inward flow of air from the external atmosphere through each of said openings effective to restrain the escape therethrough of the cloud and therewith of coating powder which has not adhered to the article, the rotational movement of the cloud serving further to restrain said escape as regards the coating powder by carrying the powder in suspension in the air past the openings.

A generally preferred embodiment of such apparatus will now be particularly described with reference to the accompanying drawings.

In these drawings:

FIGURE 1 is an external elevation of the apparatus, with a part broken away to show certain details hereinafter described;

FIGURE 2 is an end view of the apparatus, also with a part broken away to show certain details, the view looking in the direction of arrow A in FIGURE 1;

FIGURE 3 is a horizontal section through the apparatus on the section line 33 of FIGURE 1;

FIGURE 4 is a vertical section through the apparatus on the section line 44 of FIGURE 1;

FIGURE 5 is a fragmentary vertical section through a lower part of the enclosure of the apparatus in the median plane of symmetry thereof;

FIGURES 6 and 7 are sections through FIGURE 5 on section lines 6-6 and 77 of that figure;

FIGURE 8 is a control diagram, illustrating the manner of controlling the various Working components of the apparatus, the diagram viewing the apparatus from the view point of FIGURE 1; and

FIGURE 9 is a fragmentary horizontal section through one of the corners of the enclosure, illustrating a modification hereinafter described.

Like reference numerals denote like parts in the various figures.

The apparatus shown comprises a rigid boxshaped structure consisting of side walls 1, 2, end walls 3, 4, a bottom wall 5 and a top wall 6 rigidly connected together, e.g. by bolted connections so as to be readily dismemberable as necessary.

In the two end walls 3, 4 are openings 7, 8 located on the vertical centre line of the wall. Opening 7 constitutes the entry opening aforesaid and opening 8 to the exit opening. The articles to be coated therefore enter the apparatus by opening 7 and leave it by opening 8.

The articles are conveyed through these openings and along the interior space of the enclosure (later identified) upon conveyor means, which may include a rail (or the equivalent) schematically shown at 9 in FIG- URES 1 and 2. The articles are suspended from this rail by hangers (not shown) transportable along the rail, continuously or discontinuously, according to the requirements of the coating operation, in the direction of arrows B (FIGURES 1 and 3).

In the lower part of the box-shaped structure aforesaid is a V-section trough 10. This trough, with the top wall of the box-shaped structure and the portions of the side and end walls thereof defines a space which is devoid of any direct communication with the external atmosphere other than by way of the entry and exit openings 7, 8. Said space constitutes the enclosure of the apparatus, the trough 10 forming the floor of the enclosure.

At each side of the box-shaped structure, on the outside thereof, are a pair of supply troughs 11, 12 and 13, 14 for the coating powder.

At the foot of each trough is a small box 15, 16, 17 or 18. In this box is a device (not shown) for imparting vibration to the powder in the lower part of the trough, also a device (not shown) for ejecting powder from the trough to a spraying unit or units asosciated therewith. These two devices are operated by compressed air supplied to the relative box containing them from a compressed air main 19 leading to a series of control valves mounted on a control panel P affixed to side wall 1 of the box-shaped structure aforesaid, on the outside of the structure.

At each end of the box-like structure are two filter boxes 20, 21 and 22, 23. These filter boxes comprise in each case a front wall 24 consisting of a rigid frame 25 mounting a panel 26 composed of air-permeable material, e.g. air-permeable textile material, capable of intercepting, by a filtering action, very fine particles of solid material. The unit comprising the frame and the panel is mounted so as to be readily removable from place in the filter box to gain access to the interior of the box.

Located within the enclosure are two sets of spraying units, one on either side of the vertical plane of symmetry of the enclosure, in which plane, which is marked 27 in FIGURES 2 and 4, is the path of travel of the articles through the enclosure.

Each spraying unit comprises a spraying head and a carrier tube therefor. The heads of the set of spraying units which are located on the right side (looking in the direction of arrow A in FIGURE 1) of the plane of symmetry 27 are marked 28, 29 and 30. Those on the left side of said plane are marked 31, 32 and 33.

The carrier tubes of the spraying units are marked 34. Each tube extends through a gland 35 mounted for its reception on the relative side wall 1 or 2. This gland permits axial movement of the tube toward and away from plane 27 to adjust the working position of the relative spraying head with respect thereto. The gland also permits limited universal movement of the tube to adjust the working orientation of the unit to accommodate the requirements of the spraying operation, which require- 4 ments will depend inter alia upon the size, shape and general character of the articles to be coated.

The spraying heads, which are operated by compressed air, may be of any desired or necessary design and manner of operation. One suitable form of head is the form described in the specification of United Kingdom Patent No. 1,024,892. According to this form the head consists of a rotating cup surrounded by a shroud designed to produce an annular stream of air coaxial with the cup. Powder is ejected by centrifugal force from the forward edge of the cup and is directed by means of the annular stream of air towards the article or articles to be coated. Another suitable and generally preferred form is the form described in the specification of United Kingdom Patent No. 1,046,486 in which the head consists of a pair of coaxial rotating discs again surrounded by a shroud. In this case powder is ejected through a small gap between the rotating discs.

Yet another form of head is described in United Kingdom patent application No. 23,514 of 1966 in which the rotational speed of the head is capable of being varied to vary the distribution pattern of the powder.

Preferably, an electrostatic field is maintained between the discs, or as the case may be, the cup or the like and the article or articles undergoing coating, for the purpose hereinbefore described.

Spraying unit 33 is fed with coating power from supply trough 11 by way of two feed pipes 36, 37.

Spraying unit 32 is fed with coating powder partly from supply trough 11, by way of a feed pipe 38, and partly from supply trough 12 by way of a second feed pipe 39.

Spraying unit 31 is fed with coating powder from supply trough 12 by way of two feed pipes 40, 41.

Spraying units 28, 29 and 30 are similarly fed from supply troughs 13, 14 by way of feed pipes 42, 43, 44, 45, 46 and 47.

The feed pipes, which are flexible, dip deeply into the charges of coating powder in the supply troughs so as to reach down, at their inlet ends, to the boxes 15, 16, 17 aforesaid.

The compressed air for operating the spraying heads reaches the heads by way of conduits which are individually controllable by the valves above referred to on control panel P.

There are twenty of such valves marked respectively 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, each having a pressure gauge associated with it, as clearly shown in FIGURES 1 and 8.

Valves 60, 61, 62, 63 control the supply of operating air to the air flow devices in boxes 15, 16, 17 and 18, by way of pipes 81, 82, 83, 84.

Valves 64, 65, 66, 67 control the supply of operating air to the vibrating devices in these boxes, by Way of pipes 85, 86, 87, 88.

Valves 68, 69, 70, 74, 75, 76 control the supply of operating air to the motor elements of the heads of the spraying units 31, 32, 33, 28, 29 and 30 respectively, by way of pipes 89, '90, 91, 92, 93, 94.

Valves 71, 72, 73, 77, 78, 79 control the supply of compressed air to the shrouds of the heads, by way of pipes 95, 96, 97, 98, 99, 100.

Examination of the control circuit diagram (FIGURE 8) will show that the connections between the various valves on the control panel and the pipes they respectively control are as described above.

In each corner of the box-shaped structure is a motorised fan. The four fans are marked 105, 106, 107, 108, the motors of the fans being shown at 109, 110, 111 and 112.

The fans each draw air from the enclosure (above identified) and deliver it by way of a conduit 115 leading upwardly from the outlet of the fan to a device, shown diagrammatically at 116, for dividing the air stream delivered into it into two streams, 117, 118 (hereinbefore referred to as sub-streams).

Stream 117 is delivered into the relative filter box (20, 22, 23 or 24) in a condition in which it is as far as possible free from coating powder carried out of the enclosure in suspension in the air which is withdrawn from the enclosure by the fan (105, 106, 107 or 108), the device 116 being adapted to accomplish this powder separating effect in dividing the air delivered into it into the two streams 117, 118.

Stream 118 is delivered into a conduit 120 which continues for a short distance downwardly along the interior of the filter box and then turns'rearwardly of said interior into the interior space of the enclosure, where it joins a downwardly leading manifold pipe of semi-circular cross-section located adjacent one side edge of the inlet (or outlet) opening of the enclosure in the manner clearly shown. The four manifold pipes are shown at 121, 122, 123, 124.

In each manifold pipe are a number of small diameter orifices through which air passing down the pipe issues in jets into the enclosure interior. 7

The four series of jets which issue respectively from the orifices of the four manifolds are marked 125, 126, 127 and 128 and it will be seen'that jets 125 and 128 are directed towards the interior space of the enclosure along paths which are oblique to the general plane of the inlet or outlet opening 7 or 8, the jets being in each case directed towards the plane 27 aforesaid; while jets 126 and 127 are directed towards the interior of the enclosure along paths which are oblique to the portion 129, 130 of the end walls of the enclosure which are located between the entry and exit openings 7, -8 of the enclosure and the side walls 2, 3 of the enclosure.

Streams 117 fill the interior space of the filter boxes and raise the pressure therein to an extent suflicient to force the air in said space (as far as possible freed from entrained particles of coating powder, as already remarked) through the fine interstices of the panel of filtering material forming the front wall of the filter box, so denuding it as far as possible of all residual particles, even down to the finest of them, with the result that the air leaving the filter box is absolutely, or as near as possible absolutely, clean air, while the air which is recycled to the enclosure interior in the jets 125, 126, 127, 128 returns thereto, as far as possible, the whole of the coating powder that has been withdrawn from the enclosure in the air sucked out therefrom by the fans 105, 106, 107, 108

The net effect of the combined action of the four fans is therefore to produce a controllable degree of subatmospheric pressure within the enclosure, a proportion of the air withdrawn from the enclosure by the fans being ejected from the apparatus via the filter boxes 20, 21, 22, 23. This ejected air is shown by arrows 135.

As a result air is caused to flow into the enclosure from the external atmosphere by way of entry and exit openings 7, 8, the rate of inflow being proportional to the speed of the fans, which is controllable at will, by means not shown.

The inflow of air through the openings 7, -8 operates to restrain the escape of coating powder which is not adhering to the articles undergoing coating in the enclosure, as already visualised.

The powder sprayed into the enclosure forms with the air filling the enclosure a cloud composed of said air and said powder, the latter being in a state of fine suspension in the air, and the effect of the two series of jets proceeding respectively one from manifolds 121 and 124 and the other from manifolds 122 and 123 is to produce continual rotational movement of this cloud, as indicated by arrows C in FIGURE 3.

ln producing this effect the jets co-operate with an arrangement of baflles comprising a first pair 140, 141 extending part-way across the openings 7, 8 from the side thereof at which the manifold pipes 121 and 124 are situated, obliquely to the general plane of the opening 7 or 8; a second pair 142, 143 located adjacent the manifold pipes 121 and 124, and disposed obliquely to the end wall 3 or 4 of the enclosure; a third pair 144, 145 located adjacent the manifold pipes 122, 123 and also dispose-d obliquely to said end walls; and four larger bafiles 146, 147, 148, 149 located at the four corners respectively of the enclosure and spaced a short distance at the lateral edges of the bafiles from the adjacent wall of the enclosure so as to leave a narrow gap 150 at each said edge.

The triangular shaped spaces 151 behind the four baffies 146, 147, 148, 149 form pockets of interior space of the enclosure in which the air flowing through the enclosure is relatively quiescent in spite of the rotational movement aforesaid of the body of the air.

As shown, it is from these pockets that the air is drawn out of the enclosure by the fans, the inlet ends of the conduits, which are marked 150, being located respectively in the four pockets, just above the outer marginal portions of the V-section trough 10.

The particles of coating powder which refuse to adhere to the article or articles undergoing coating in the enclosure tend to collect on the upper surface of the trough 10, also on the interior surfaces of the walls of the enclosure from which they gravitate down onto said upper surfaceeventually reaching the bottom of the trough where they collect along the bottom of the V.

From this position they are removed by air ejectors which recycle the powder to the six spraying heads of the apparatus by way of conduits 161.

The six ejectors 160 are fed with collected particles by air jets 162 delivered through orifices in a pair of manifold pipes 163, 164 located a short distance above the bottom of the trough lengthwise of the latter. The effect of these jets is to propel the particles along the bottom of the trough towards a bafile plate 165 which with the adjacent portions of the bottom of the trough forms a pair of collection sumps for the particles from which the latter are removed by the ejectors 160, the action of the ejectors being assisted by further jets 166 proceeding from orifices in four transverse manifold pipes 167, 168, 169 and 170 fed with compressed air from manifold pipes 163, 164 by way of junction pipes 171, 172. These four transverse manifold pipes additionally serve as supports for the manifold pipes 163, 164 at the ends thereof adjacent the baffle plate 165, supporting them, as shown, from the sides of the trough 10.

At each side of the box-shaped structure, beneath the trough 10 at the two sides thereof, is a recess housing a high tension current generator 181 and a distributor 182. The distributor has three output terminals 183, 184, 185. These terminals, of each distributor, are connected by current leads 186, 187, 188 to the three spraying heads on the side of the apparatus at which the relative distributor is situated. This again is clearly apparent from FIGURE 8 wherein the current leads 186, 187 leading to spraying heads 31, 32, 33 are shown in full lines and those leading to spraying heads 28, 29, 30 are shown in broken lines.

Likewise in FIGURE 8, the various pipes leading from the control panel to spraying heads 31, 32, 33 and the two boxes 15, 16 at the bottom of supply troughs 11, 12 are shown in full lines while those leading to spraying heads 28, 29, 30 and boxes 17, 18 are shown in broken lines.

The hangers (or their equivalent) upon which the articles are to be coated are conveyed through the apparatus travel along a suitable opening (e.g. a slot) provided for their accommodation in the top wall 6 of the box-shaped structure. It is necessary to seal this opening as efiiciently as is practicable in order to minimise the escape of coating powder therethrough to the external atmosphere. For this purpose, in the particular embodiment of the invention illustrated, overlapping flexible strips 190, 191 are provided to cover the opening, the strips being adapted locally to part at their mutually overlapping edges wherever along the opening a hanger happens to be located.

Similar sealing means are provided above the entry and exit opening 7, 8, it being necessary, as will be understood, to provide openings in the end walls 3, 4 of the boxshaped structure, to accommodate the passage of the hangers therethrough.

In place of sealing means as described the openings in the top wall and end walls of the box-shaped structure which accommodate the passage of the hangers, means similar in principle to those which are employed for preventing egress of air from the enclosure through the entry and exit openings 7, 8 may be employed.

Referring now to FIGURE 9, the modification there shown concerns the filter boxes and manifolds in the four corners of the enclosure.

According to this modification the manifolds form part of the rear wall 190 of the filter box, the interior space of which is subdivided by a partition 191 integral with rear wall 190 into two sections 192, 193. Section 192 has the filtering panel of the box extending across it, this panel being similar to the panel 26 of the filter boxes of the earlier construction, and houses the device which divides the stream of air withdrawn from the enclosure interior into two sub-streams. Section 193 forms a manifold into the which sub-stream 118 is delivered by way of a conduit 194. Said device is marked 116 and the two sub-streams are marked 117, 118. Sub-stream 118 is delivered into the manifold 193, from which it flows into the enclosure interior in the form of jets 195 by way of holes 196 in a thickened portion 197 of rear wall 190. The jets correspond to the jets 125, 126, 127 and 128 shown in FIGURE 3 and the holes 197 are at a predetermined inclination to the general plane of rear wall 190, according to the required obliquity of the paths of the jets, Also in the two filter boxes at respectively transversely opposite corners of the enclosure the holes occupy the full line positions, so as to direct the jets towards the vertical central plane of the enclosure, while in the other two filter boxes they occupy the dotted line positions, so as to direct the jets away from said plane-in correspondence in this respect to the directions in which said jets 125, 126, 127 and 128 of the earlier described construction fiow into the enclosure.

Such a construction is advantageous over a construction in which the manifolds take the form of half-round section pipes located within the enclosure against the end wall thereof, in that it avoids the presence of crevices between the manifold and the face of said end wall, in which powder can collect and possibly set up trouble, for example in changing over, in the use of the apparatus from coating in one colour to coating in another colour. Also by removing the front cover of the manifold section of the filter box, which is detachably mounted for this purpose, it is possible to gain immediate access to the jet holes for cleaning or other attention. A

further advantage is that owing to the greater length of the jet holes as compared with a construction as illustrated in the earlier figures, better jet definition is obtainable. Finally, with the construction illustrated in FIGURE 9 the filter box actually forms part of the end wall of the enclosure, thus simplifying the construction.

It will thus be seen that the invention provides a simple and effective solution to the problem of preventing the escape of coating powder from an enclosure in which a powder coating operation is performed.

Finally, various modifications as regards constructional details of the coating apparatus are possible within the general scope of the invention. For example the enclosure may be of any other convenient geometrical form; the spraying heads may be mounted in any other convenient way than that shown in the drawings; the air withdrawal means may be different, as also may be the design and position of the filter boxes. Likewise the control panel and its connections may be difierent from that shown.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A method for applying powder particle coatings to articles comprising conveying the articles into an enclosure provided with entry and exit openings on Opposite sides of the enclosure, spraying the articles with a plurality of streams of coating powder particles by spraying jets located transverse to the path of travel of the articles in sufiicient quantity to form with the air in the enclosure a fine cloud of the powder particles suspended in the air, directing a plurality of jets of air toward said cloud to impart a continuous rotational movement about a substantially vertical axis extending transversely with the path of travel of the article, Withdrawing a portion of said cloud thereby producing subatmospheric pressure in the said enclosure and causing an inward flow of air through the said openings to prevent the escape of the excess powder particles and removing the coated article from the enclosure.

References Cited UNITED STATES PATENTS 1,263,858 4/1918 Cole 1l8309 X 2,086,514 7/1937 Saunders et al 117-102 2,324,784 7/1943 Lundgren 11719 3,013,891 12/1961 Block 11719 3,108,022 10/1963 Church 17--21 X 3,291,630 -12/1966 Deyle et al. 11719 X 3,323,934 6/1967 Point 117-17 2,806,803 9/1957 Thackara 1l7-17 3,208,868 9/1965 Strobel et al 1l7-94 1,088,874 3/1914 Bradley 11724 WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R. 

